An acceleration sensor, a gyroscope, a displacement sensor, a pressure sensor, or other type of physical sensor for detecting a physical change as a capacitance change, is required to reduce circuit noise when a capacitance detection circuit thereof needs to have a high resolution or when a MEMS (Micro Electro Mechanical System) sensor needs to be combined with the capacitance detection circuit in order to achieve cost/size reduction.
As such a capacitance detection circuit, there is known, for example, a capacitance detection circuit in which a sensor drive circuit applies drive voltage to a capacitance sensor element, a change in capacitance of the sensor element is converted into a voltage signal by a continuous-time C-V conversion circuit, a synchronous detecting circuit detects a signal component from a voltage signal obtained as a result of the conversion, and a smoothing circuit smoothes an output signal of the synchronous detecting circuit (see Patent Document 1, for example).
Patent Document 1: Japanese Patent Application Publication No. 2011-107086
Incidentally, the prior art described in Patent Document 1 is capable of accurately obtaining a detected output as an analog signal even when the capacitance changes continuously and slightly in response to a quantity change. When obtaining a detected output as an analog signal, the sensor drive circuit supplies sensor drive signals to a detection capacitor (capacitance Cs) and a reference capacitor (capacitance Cr), wherein the sensor drive signal is inverted in phase in order to be supplied to the reference capacitor (capacitance Cr). The sensor drive signal supplied to the detection capacitor (capacitance Cs) and the sensor drive signal supplied to the reference capacitor (capacitance Cr) are added up, and the difference therebetween is supplied to a charge amplifier.